全文获取类型
收费全文 | 52593篇 |
免费 | 5559篇 |
国内免费 | 3201篇 |
专业分类
电工技术 | 1458篇 |
综合类 | 4137篇 |
化学工业 | 9920篇 |
金属工艺 | 5816篇 |
机械仪表 | 5648篇 |
建筑科学 | 2978篇 |
矿业工程 | 1835篇 |
能源动力 | 1478篇 |
轻工业 | 6583篇 |
水利工程 | 1500篇 |
石油天然气 | 1499篇 |
武器工业 | 516篇 |
无线电 | 4368篇 |
一般工业技术 | 7556篇 |
冶金工业 | 1737篇 |
原子能技术 | 533篇 |
自动化技术 | 3791篇 |
出版年
2024年 | 236篇 |
2023年 | 1038篇 |
2022年 | 1425篇 |
2021年 | 1826篇 |
2020年 | 1972篇 |
2019年 | 1819篇 |
2018年 | 1774篇 |
2017年 | 2082篇 |
2016年 | 2056篇 |
2015年 | 2180篇 |
2014年 | 2872篇 |
2013年 | 3693篇 |
2012年 | 3908篇 |
2011年 | 4029篇 |
2010年 | 2801篇 |
2009年 | 2809篇 |
2008年 | 2620篇 |
2007年 | 3289篇 |
2006年 | 3006篇 |
2005年 | 2447篇 |
2004年 | 2007篇 |
2003年 | 1696篇 |
2002年 | 1540篇 |
2001年 | 1264篇 |
2000年 | 1160篇 |
1999年 | 960篇 |
1998年 | 782篇 |
1997年 | 734篇 |
1996年 | 651篇 |
1995年 | 480篇 |
1994年 | 436篇 |
1993年 | 364篇 |
1992年 | 293篇 |
1991年 | 197篇 |
1990年 | 206篇 |
1989年 | 136篇 |
1988年 | 135篇 |
1987年 | 63篇 |
1986年 | 81篇 |
1985年 | 65篇 |
1984年 | 58篇 |
1983年 | 46篇 |
1982年 | 44篇 |
1981年 | 13篇 |
1980年 | 21篇 |
1979年 | 15篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1959年 | 7篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Four epoxy film adhesives used in aircraft manufacture and repair have been examined to establish the effect of deviation from the cure cycle specified by the manufacturer. In addition to the variation of the cure cycle, two surface preparations of the aluminium adherends (chromic acid etch or grit blast followed by silane treatment) were evaluated. Thermal analysis was used to examine the cure envelope of the adhesive, and its extent of cure and glass transition temperature. The adhesive properties were assessed by shear strength (in both single lap joints and in Iosipescu configuration), durability (Boeing wedge test) and chemical resistance to selected aggressive fluids. The sensitivity of the performance of a particular adhesive to offoptimum cure conditions depends on its composition and needs to be determined, not predicted. 相似文献
182.
In the absence of a bulk diffusion effect, it is shown for the first time that the impedance spectra for the chlorine evolution reaction on a rotating thin ring electrode comprise three consecutive semicircles in the capacitive half of the complex plane. The first (highest frequency) semicircle is due to the charge-transfer resistance for chloride discharge and the simultaneous chlorine adsorption coupled to the double-layer capacitance. The second semicircle (around 5 Hz) is due to the adsorption and desorption of a chlorine intermediate. The third (lowest frequency, around 0.5 Hz) semicircle is due to the relaxation of surface oxygen species. The impedance data allow the steps of the overall reaction to be examined individually. On a Pt surface the rate of chloride discharge and simultaneous chlorine adsorption (the admittance of the first semicircle) is first order with respect to chloride concentration and has a potential-dependence close to 58 mV/decade. The rate of the adsorption and desorption process (the admittance of the second semicircle) is second order with respect to chloride concentration, and has a potential dependence close to 30 mV/decade. The time constant for the adsorption/desorption processes is ca 20 ms, independent of electrode potential in the range studied. These features are consistent with a mechanism in which a faster discharge reaction (Cl− Clad + e) is followed by a slower surface combination reaction (2Clad → Cl2), but inconsistent with mechanisms in which ion + atom desorption is predominant, the initial chloride discharge is slow, or a unipositively charged chlorine species is involved. 相似文献
183.
航空齿轮表面硬化层断裂性能研究 总被引:1,自引:0,他引:1
按照航空齿轮的具体工艺过程,对材料12Cr2Ni4A的拉伸试样和断裂试样进行设计和加工,通过三点弯曲实验,重点研究了齿轮材料硬化层的硬度分布,硬化试样拉伸力学性能参数和断裂性能参数,实验结果表明,所采用试样的加工工艺方案是可行的,所获得的Kc基本反映我国航空硬化齿轮材料的断裂性能特征,为定量预测航空硬化齿轮疲劳寿命提供实验和理论分析的依据。 相似文献
184.
撞击流管式反应制备超细氧化锆粉体 总被引:6,自引:0,他引:6
我国氧化锆粉体产业目前基本上“精进粗出”,迫切需要开发氧化锆粉体备新工艺,特别是具有高附加值的纳米氧化锆粉体制备技术,液相反应沉淀法具有成本低,易于工业化等优点而成为研究的热点。本文采用撞击流管式反应新工艺,撞击流接触反应强化了过程的微观混合。实现了均匀成核,使得成核过程易于控制,而管式反应器的独特设计克服了返混,因而使得反应沉淀过程易于控制,粒子分布窄。用该工艺结合醇热处理表面改性制备的超细氧化锆粉体。平均粒径约为14nm,粒度分布窄并无硬团聚发生。该方法过程简单,易于工业化大生产。 相似文献
185.
优化SMC模压工艺控制制品收缩率和表面粗糙度 总被引:1,自引:0,他引:1
优化SMC模压工艺参数:模压压力分为二阶段,选定最佳压力释放时机和压力;适宜降低模压温度。可显著降低SMC制品的固化收缩率,提高其表观质量、试验表明,同时采用的线收缩率和表面粗糙度两种检测和村定方法具有很好的同一性。 相似文献
186.
化学氧化法制备的聚苯胺表面的亲水性差,本文在本征态和不同酸掺杂志聚苯胺的表面上接枝共聚丙烯丙烯酸和丙烯酰胺,明显地改善了聚苯胺的表面亲水性。结果显示,聚苯胺表面经过等离子体处理后,有利于丙烯酸和丙烯酰胺在聚苯胺表面上的接枝共聚,随着接枝量增多,导电率则随之有所下降,此外,利用SEM和反射IR表征了改性反聚苯胺表面的形态和结构。 相似文献
187.
188.
189.
Amjad B. Soulaka William R. Morrison 《Journal of the science of food and agriculture》1985,36(8):709-718
Starches isolated from 23 bread wheats (Triticum aestivum) and 26 durum wheats (T. durum) contained 26.3-30.6% (mean 29.1%) total amylose, 19.3–25.1% (mean 22.9%) apparent amylose and 783–1144mg 100g?1 (mean 977 mg 100g?1) lysophos-pholipids. Gelatinisation temperatures were 57.3–64.9°C (mean 61.8°C) and enthalpies 6.4–11.8 Jg?1 (mean 9.7Jg?1) in excess water, measured by differential scanning calorimetry. There were no correlations between any of these parameters. Starch granule size distributions were determined with a Coulter Counter and 100–channel analyser. A-granule mean volumes were 1235–2585μm3 (av. 1778), modal volumes 863–1804μm3 (av. 1264), mean diameters 13.9–16.0μm (av. 13.99), and specific surface areas 0.236–0.302m2g?1. B-granule mean volumes were 35.4–100.4μm3 (av. 55.9), modal volumes 16.5–54.5μm3 (av. 27.7), mean diameters 3.66–5.07μm (av. 4.09), and specific surface areas 0.684–0.920m2g?1. The B-granule contents of the starches were 12.8–34.6% (av. 27.3) by weight (sedimentation method) and 13.0–37.3% (av. 24.0) by volume (Coulter method), the latter being the more accurate method. 相似文献
190.
CAMILA DUARTE TELES SIMONE HICKMANN FLÔRES 《International Journal of Dairy Technology》2007,60(4):270-276
In this work, response surface methodology was applied to a study of the effects of the addition of skim milk powder and stabilizers on the apparent viscosity and sensory attributes of nonfat yogurt. The addition of stabilizers has been shown to produce a significant effect on sensory attributes, while high concentrations of xanthan and guar gum are seen to decrease the overall acceptability of the yogurt, with gelatin producing the higher apparent viscosity and consistency. The correlation among apparent viscosity, which is an instrumental measurement, and consistency, which is a sensory evaluation, was 0.72. 相似文献